I use ro water in my tank now after some time of useing a hmv filter. I use Tropic marine pro- discus to remineralize the water and get a ph reading of 6.8 however when I test for my kh I only get a reading of one!! If I understand correctly to increase my kh will also increase my ph, yet I read other poaple who say they have a kh of say 5 with a ph of 6.4 how can this be sorry I am a bit thick but I am so scared of ph crash and I want to make sure my water is stable Please can you advise

I not a water expert and I personally keep things as basic as possible, due to this I'm not a fan of using minerals to re-vitalise pure RO water. I would prefer to get a bag of crushed coral into the tank (or filter) to act as a buffer. This will depend of course on the tank size, stocking level, water changes etc etc. Therefore if you use pure RO and a have a heavily stocked tank, feed heavily and don't keep on top of the w/c's then even a large bag of crushed coral will not save you. The organics will cause the ph to lower.

Far too often I think people get hung up on maintaining a ph of 6.5 or whatever............Discus DO NOT NEED a low ph........they prefer soft acidic water but even wild fish can get used to a neutral ph. The super soft water is only required for breeding. The main thing discus require IMO is stability. A stable ph and stable water parameters are more important than a ph of a certain value.

The theory is the higher the dKH the higher the pH will be, but in practice this is not always the case - as Tony has posted something to do with an enclosed small body of water, biological filtration and so on.

With regard to the Tropic Marin Discus Pro - does indeed add little or no KH to the water, but their product Tropical re-min does.

What more and more people are doing is mixing the two products 50/50 and report back being very satisfied with the water it produces.

As ever with water chemistry, different things work for different areas (source water being inconsistent) so a morning spent experimenting is worth it's weight in gold.

Hudson's lecture in Sweden put a few myths to bed, he catches wild Discus then QTs and acclimatises them in Conductivity 300ms and pH of 7....there are many paths to the top of a mountain..

Thanks for all your advice, I have spent the day testing . In my ignorance I thought that marine discus would give me all I needed to balance my ro water but thanks to marks suggestion I now reralize my mistake,